So how do events play out in a normal breeding season? A clear model of what happens can be seen with snow and Ross's geese nesting at the large Karrak Lake colony south of Queen Maud Gulf in Canada 's central Arctic. Dr. Ray Alisauskas of the Canadian Wildlife Service has studied these geese for the past 16 years. In an average year, the first snow geese arrive by June 1, and the first Ross's geese, about three days later. However, the average date of nesting at the Karrak Lake colony is about June 11. In any given year, all nests are started over a range of about three weeks—a synchrony imposed by short Arctic summers. If conditions are ideal, the first eggs are in nests the day after the birds arrive. By June 16, incubation starts on the average full clutch of 3.5 eggs. Average hatch occurs on July 3. The first Ross's geese are flying by August 15, and the first snow geese by August 22. The young of both species can sustain flight by August 31, just ahead of the first major freeze of the year between September 10 and 15, when most geese leave the Arctic for the prairies.
This remarkable series of events has been compressed into just over 90 days. But not all goes so smoothly every year. In late springs when cold and snow persist, the birds can't start nesting immediately because their eggs will freeze. They must use fat reserves simply to sustain their own lives. This is a necessary trade-off between energy for survival and energy for reproduction. As time goes by, fat reserves get smaller until about the third week of June, when it is no longer worth trying to nest because the young will not have time to mature enough to fly south. For the few geese that try, their young may die right on the breeding colony or en route to the Canadian prairies. Geese stubborn enough to nest late put their own lives at risk because they may become too emaciated to make it across the boreal forest. Natural selection is very tough on birds that make such mistakes.
A late spring on the Arctic breeding grounds typically leads to a challenging fall for hunters because having few young in the flocks makes it much more difficult to attract birds within shooting range. Every adult has had at least seven months of experience the previous year with decoy spreads and goose calls, so they are wary of joining other birds on the ground, as they may not actually be geese. The average snow goose lives another seven years once it survives the first year of life. These old-timers have accumulated at least 49 months of experience flying from roosts to feeding areas where hunters may wait. Making mistakes here can be deadly too, so most of these survivors know how to avoid decoy spreads.
The pattern at Queen Maud Gulf is repeated on all goose colonies across the northern breeding areas from Baffin Island to Alaska's North Slope to the Hudson Bay Lowlands and northern Quebec. From year to year, the unforgiving northern climate is the most important single variable that affects the size and age structure of the fall flight of Arctic geese.